Typical materials requiring surface flatness at high level include a single-crystal silicon disk called a silicon wafer for producing semiconductor integrated circuits (IC, LSI). The surface of the silicon wafer should be flattened highly accurately in a process of producing IC. LSI etc., in order to provide reliable semiconductor connections for various coatings used in manufacturing the circuits. In the step of polishing finish, a polishing pad is generally stuck on a rotatable supporting disk called a platen, while a workpiece such as a semiconductor wafer is stuck on a polishing head. By movement of the two, a relative speed is generated between the platen and the polishing head while polishing slurry having abrasive grains is continuously supplied to the polishing pad, to effect polishing processing.
The polishing pad used is preferably made of a polyurethane foam. For example, the following methods are proposed to produce such a polyurethane foam.
There is proposed a method including providing a mold under the bottom of a tank, injecting a polyurethane foam-forming composition into the mold from the tank through a valve provided at the bottom of the tank, and performing reaction and curing of the injected polyurethane foam-forming composition to form a polyurethane foam (Patent Document 1).
Unfortunately, the method of Patent Document 1 has a problem in that when the polyurethane foam-forming composition has high viscosity or high thixotropy, the composition is difficult to be well discharged through the valve, and thus the composition can cause clogging, or a raw material or a cured product can adhere to the inside of the valve and then enter the composition, so that the quality of the product can degrade or air voids can easily form during the process of injecting the composition into the mold through the valve.
There is also proposed a method of producing a molded resin product, which includes a first step of adding, to a tank, a liquid raw material for use in forming a molded resin product; and a second step of pouring the liquid raw material from the tank into a mold and curing it, wherein the first step is performed while the opening formed at the side of the tank is closed with a door member, and the second step includes opening the door member to open the opening so that the liquid raw material for use in forming the molded resin product is poured into the mold placed below the opening (Patent Document 2).
However, the method of Patent Document 2 also has a problem in that when the liquid raw material for use in forming a molded resin product has high viscosity or high thixotropy, air voids can easily form during the process of pouring the liquid raw material into the mold. There is also a problem in that the raw material can adhere to the inner wall of the door member and then often drip onto the liquid surface, which can often degrade the product quality of a molded resin product.